Oracle's two major index types areBitmap indexesandB-Tree indexes. B-Tree indexes are the regular type thatOLTP systemsmake much use of, and bitmap indexes are a highly compressed index type that tends to be used primarily fordata warehouses. Characteristic of Bitmap Indexes For columns wit...
CREATE_BITMAP_AREA_SIZE是Oracle定义每个SGA中用于创建和维护位图的内存区域的一个参数,它的值默认为0MB,也就是说,在默认条件下,Oracle没有在SGA中专门分配用于位图的内存区域。如果该参数被设置为非0值,那么Oracle将会在SGA中创建一个名为“Create Bitmap”的内存区域,来储存位图;而且,Oracle会优先在该区域中创...
(1) bit in one and only one of the bit vectors. Now we search using the bitmap index. SELECT COUNT(*) FROM T WHERE C IS NULL; ... Do this by counting the 1 bits in the NULL bit vector. The good things that we can note from this example are that the index is small (a ...
A method and apparatus for segmenting bitmaps in a bitmap index is provided. A segmented bitmap includes a plurality of bitmap segments that are used to indicate which records in a body of records that is associated with the segmented bitmap satisfy a particular criteria. Each bitmap segment...
What we see here is that (unhinted) oracle has converted the IN subquery to an EXISTS subquery then to a semi-join which it has chosen to operate as a HASH semi-join. But in the process of generating the probe (sescond) table Oracle has converted the bitmap index entries into a set...
Oracle recommends that you enable automatic sizing of SQL working areas by setting PGA_AGGREGATE_TARGET instead. CREATE_BITMAP_AREA_SIZE is retained for backward compatibility. A larger value may speed up index creation. Cardinality is the number of unique values in a column in relation to the...
rank(2); // would return the rank of 2, which is index 1 rr.contains(1000); // will return true rr.contains(7); // will return false RoaringBitmap rror = RoaringBitmap.or(rr, rr2);// new bitmap rr.or(rr2); //in-place computation boolean equals = rror.equals(rr);// ...
这个方法将bitIndex位上的值由false设置为true,解释如下: 我们设置的时候很明显是在改变long数组的某一个元素的值,首先需要确定的是改变哪一个元素,其次需要使用与或操作改变这个元素,在上面的代码中,首先将bitIndex>>6,这样就确定了是修改哪一个元素的值,其次这里涉及到一个expandTo方法,我们先跳过去,直接看代码...
(2);// would return the rank of 2, which is index 1rr.contains(1000);// will return truerr.contains(7);// will return falseRoaringBitmaprror=RoaringBitmap.or(rr,rr2);// new bitmaprr.or(rr2);//in-place computationbooleanequals=rror.equals(rr);// trueif(!equals)thrownewRuntime...
Bitmap index compression United States Patent 6205442 Abstract: A method and apparatus for compressing data is provided. The invention compresses an input bit stream into a compressed output bit stream. The input bit streams are byte aligned and classified. Bytes with all bits set to value zero...